The need for deicing aircraft prior to flight has long been recognized. Several mechanical methods have been proposed. For example, U.S. Pat. No. 4,895,322 discloses the use of an electrically induced magnetic force to de-bond ice from the surface of an aircraft. U.S. Pat. No. 5,035,380 teaches a deicer system which features the use of resilient inflatable tubes on the leading edge of an aircraft wing. The tubes break up ice by undergoing a series of inflations and deflations. U.S. Pat. No. 5,074,497 discloses the use of deicer pads on aircraft which physically dislodge ice from an aircraft after being activated by an electromagnetic field pulse generator.
Some methods for chemically deicing aircraft have also been proposed. Glycol solutions are most frequently used for this purpose, though other suitable compositions have been suggested (see, e.g., U.S. Pat. No. 4,954,279). For example, U.S. Pat. No. 4,898,330 teaches the use of a portable hose-and-tank type sprayer to apply a glycol solution to aircraft. U.S. Pat. No. 5,104,068 (Krilla et al) discloses a deicing apparatus featuring sets of nozzles arranged on booms that can be situated above and below the wings of an airplane.
Chemical methods are often preferred for deicing aircraft, partly due to their ease of use and the fact that they can be used without physical modification of the aircraft. However, many known chemical methods are inefficient because they use more solvent than is necessary to deice the aircraft. For example, the apparatus disclosed in U.S. Pat. No. 3,533,395 (Yaste) contains banks of nozzles which discharge a glycol solution. The nozzles are activated all at once, despite the fact that the wing configuration of a particular aircraft may result in some of the nozzles discharging solvent into empty space. The resulting waste of solvent increases the cost of the method and contributes to pollution. If the nozzle bank is tailored to the specifications of a particular aircraft, then the versatility of the apparatus is lost. U.S. Pat. No. 4,898,330, which features a hand held hose-and-tank type of apparatus, avoids these particular problems, but also lacks the convenience of automation and results in exposure of workers to the toxic solvents typically used to deice airplanes.
Because of the cost and pollution concerns associated with the use of glycol and other deicing solvents, various methods have evolved for recycling glycol after use. For example, U.S. Pat. No. 3,533,395 (Yaste) and U.S. Pat. No. 5,104,068 (Krilla et al) disclose methods for collecting, distilling, separating, filtering, and recycling used glycol and water. However, these methods of recycling glycol have proved inefficient in practice.
Finally, the prior art discloses a variety of deicing devices capable of installation along the taxiway of an airport. However, these devices create a significant runway hazard in that they are permanently installed above the ground. The problem is especially serious in emergency situations or when the airport must service aircraft requiring extra clearance. Mobile deicing units avoid some of these problems, but lack the convenience of permanent deicing units installed along the taxiway.